Automotive vehicles typically have a drive train in which an internal combustion engine provides power to wheels, or other motivational mechanisms, through a transmission that provides speed and torque conversions from a rotating drive shaft to the wheels using gear ratios. Typical transmissions have included combinations of planetary gears and clutches that are utilized to fix one set of gears with respect to the other gears to select one of a few predetermined ratios in a stepwise fashion.
More recently, the continuously variable transmission (CVT) has emerged in various forms (e.g., belt drive, pulley drive, etc.) to provide stepless change through an infinite number of effective gear ratios between maximum and minimum values. The flexibility of a CVT allows the driving shaft to maintain a constant angular velocity over a range of output velocities. This constant angular velocity can provide better fuel economy by enabling the engine to run at its most efficient revolutions per minute (RPM) for a range of vehicle speeds. Alternatively it can be used to maximize the performance of a vehicle by allowing the engine to turn at the RPM at which it produces peak power.
A specific type of CVT is the infinitely variable transmission (IVT), in which the range of ratios of output shaft speed to input shaft speed includes a zero ratio that can be continuously approached from a defined “higher” ratio. A zero output speed (low gear) with a finite input speed implies an infinite input-to-output speed ratio, which can be continuously approached from a given finite input value with an IVT. Low gears are a reference to low ratios of output speed to input speed. This low ratio is taken to the extreme with IVTs, resulting in a “neutral”, or non-driving “low” gear limit, in which the output speed is zero. Unlike neutral in a normal automotive transmission, IVT output rotation may be prevented because the backdriving (reverse IVT operation) ratio may be infinite, resulting in impossibly high backdriving torque. However, ratcheting IVT output may freely rotate forward.